And tennis legend Boris Becker has kick-started the debate about how he sees the ‘Big Four’ faring during the American hard-court season and beyond.

A resurgent Roger Federer and Rafael Nadal have shared the three Grand Slam titles between them during 2017, with Andy Murray and Novak Djokovic both struggling for fitness and form.

Becker hopes Djokovic can return to full fitness (Picture: Getty)

After Federer lifted a record eighth Wimbledon title, Becker believes he’s set to add a 20th major to his collection by the end of the year.

And he’s backing him to pip Nadal to the year-end world No. 1 spot.

‘Looking at the state of tennis: the top two are Roger and Rafa and it will be those guys battling it out to be world No. 1 at the end of this year,’ he wrote in the Evening Standard. ‘Most players don’t give themselves enough time off. I think more will now.

Becker views Nadal as a threat on hard courts (Picture: AFP/Getty)

‘In that battle for No. 1, Rafa is a little ahead but it’s all to play for at the US Open and the rest of the American hard-court season. The hard courts are a great leveller, so it increases Rafa’s chances over Roger but a healthy Novak and Andy will be closer to Roger on the grass, too, and more of a potential threat.

‘Who will be the favourite? That’d absolutely be Roger. From what we’ve seen this year from the two renaissance men of tennis, this should be a wake-up call for locker room and I want to see what the rest of the competition does.